When a driver is seated in a vehicle, he should adjust all of the interior and exterior rearview mirrors according to his need. The rearview mirror can be adjusted manually or automatically by pushing buttons. After the adjustment of rearview mirrors is done, the view angle of each rearview mirror seen by the driver is constant, and it is difficult and also dangerous for the driver to further change the view angles while driving.
In practice, when a driver would like to change to another lane, turn to another direction or overtaking a car, he will need to realize more about the situation of the adjacent lane to see whether there is any vehicle oncoming. Therefore, the horizontally turning of the rearview mirror toward the target lane will be helpful for the lane-changing or overtaking operation. In addition, while moving up or down a slope, it is advantageous to turn the rearview mirror vertically to obtain a view range similar to that on the flat road.
Aside from the above situations, there are more situations needing a proper view range different from that required in the normal driving mode.